II. LENGTH. 55 



In order to eliminate a source of many errors the eye-piece is fixed in the 

 telescope, and the whole cathetoineter has to be put at the required distance 

 from the object to be observed. 

 ^ The telescope is provided with a micrometer screw, 



258. Great Cathetoineter, for reading differential levels 

 more than a metre apart. 



Geneva Association for Constructing Scientific Instruments. 



This instrument is composed of a tripod supporting a central rod, which 

 bears on its upper part the brass column, that is, the prismatic piece, along 

 which the telescope moves in a parallel line. The dimensions of the column 

 are great, so as to avoid all flexure. The division on the silver plate is in 

 millimeters, and the vernier of the sliding carriage registers to the 50th of a 

 millimeter. This instrument has two levels ; the one placed between the 

 rings that support the telescope, the other placed perpendicularly to the first 

 upon the table situated at the base of the column. 



The universities of Berlin, Kome, Dprpat, Neuchatel, &c. have this 

 instrument. 



273. Cathetoineter, by Casella. The telescope moves on a 

 girder-shaped brass bar, to which the scale is attached, and is 

 furnished with a micrometer eye-piece, by means of which readings 

 can be taken without moving the telescope. The instrument is 

 supported by a massive iron frame-work. 



Prof. A. W. Rucker, Leeds. 



292. Cathetoineter. C. Bamberg, Berlin. 



The principal division of the instrument is executed on silver from centi- 

 meter to centimeter. A division into single millimeters has been made on a 

 lid connected with the principal slider, whose surface of division is on a level 

 with that of the centimeter graduation. The millimeter lid moves with the 

 principal slider, which carries the means for reading and adjustment (micro- 

 scope and telescope). The reading of the meter-division is effected (as far 

 as 0-001 mm.) by means of the ocular screw micrometer of the microscope. 

 The micrometrical displacement of the principal slider, which balances per- 

 fectly around the longitudinal axis of the scale prism, takes place by a pecu- 

 liar contrivance, which avoids all one-sided pressure. The slider with the 

 cramp operation is balanced by a counter-weight suspended from the ceiling 

 or a trestle, so that its ascending and descending motion is effected with great 

 facility. 



294. Photograph of a Cathetoineter, made by Staudinger 

 and Co. C. Staudinger and Co. (F. W. von Gehren}, Giessen. 



The peculiarities of the construction may be learned from the photo- 

 graphs. The instrument has a useful division of one meter length ; the prism 

 with the counter-weight turns completely around the long vertical axis ; the 

 prism is provided with adjusting appliances which render the direction of the 

 same to every side possible ; reversional telescope and water-level. 



3O5. Cathetometer. 



Prof. Baron von Feilitzsch, Greifswald. 



The cathetometer consists of a central axis, and a prism turning round 

 the same. For placing the central axis in a vertical position a cylindrical 

 water-level, indicating 10 seconds, is employed. A silver scale of one meter 



